Abstract
This paper presents a new constant frequency, direct grid-connected wind-based induction generator system (IGS). The proposed system includes a six-phase cage rotor with two separate three-phase balanced stator windings and a three-phase SV-PWM inverter which is used as a STATCOM. The first stator winding is connected to the STATCOM and is used to excite the machine. The main frequency of the STATCOM is considered to be constant and equal to the main grid frequency. In the second stator winding, the frequency of the induced emf is equal to the constant frequency, so the generator output frequency is independent of the load power demand and its prime mover speed. The second stator winding is directly connected to the main grid without an intermediate back-to-back converter. In order to regulate the IGS output active and reactive power components, a sliding mode control (SMC) is designed. Assuming unbalanced three-phase voltages for the main grid, a second SMC is developed to remove the machine output’s negative sequence currents. Moreover, a conventional PI controller is used to force the average exchanging active power between the machine and STATCOM to zero. This PI controller generates the reference value of the rotor angular speed. An adjustable speed pitch angle-controlled wind turbine is used as the IGS’s prime mover. The effectiveness and capability of the proposed control scheme have been supported by the simulation results.
Highlights
The use of wind energy by the electrical power generation industry has significantly enhanced in the past two decades
Considering the 1.8 kW six-phase cage-rotor induction generators (CRIGs) shown in Table 1 with a regulated speed wind turbine based on a pitch angle controller [34] and the mentioned theory in the previous sections, a C++ computer program, using the static fourth-order Runge–Kutta method, was developed to solve nonlinear differential equations of the machine
The first stator winding set is connected to an SV-PWM inverter, operating as a STATCOM, to excite the machine
Summary
The use of wind energy by the electrical power generation industry has significantly enhanced in the past two decades. Use of wind energy conversion systems (WECSs) for distributed generation, especially in remote areas with weak networks, has grown significantly [1]. The magnetizing reactive power of CRIGs has to be supplied by a reliable source [6]. These problems can be directly solved by using a full-rate intermediate BTB converter. Such BTB converters are expensive, especially in high-power rating systems. Some solutions were proposed in the literature to solve the mentioned problems, there is a need to introduce a CRIG-based system that produces an intrinsically constant frequency, independent of the prime mover speed and the load power demand. The converted energy supplied the local load or the main grid can be achieved without a BTB converter
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